Fewer U.S. workers are moving around the country to seek new job opportunities, as changing family ties and more openings near home make people less willing to uproot their lives for work.

About 3.5 million people relocated for a new job last year, according to U.S. census data, a 10% drop from 3.8 million in 2015. The numbers have fluctuated between 2.8 million and 4.5 million since the government started tracking annual job-related relocations in 1999—but have been trending lower overall, even as the U.S. population grew...